Knowledge as to the state of a person's mind is useful in several applications. In anesthesiology, the anesthesiologist typically administers a light anesthesia to make the patient sleep, administers a narcotic to prevent the patient from waking up from the pain that would otherwise arise from an operation, and administers a drug that relaxes or paralyzes the patient to prevent his muscles from reacting to stimulation from the operation procedure. In this situation, it is often found useful to detect the patient's brainwaves as by use of an electroencephalograph and to apply the brainwaves to a Fourier analyzing device that shows the amplitude of various frequencies present in the brainwaves. Both the encephalograph and the display on the Fourier analyzing device are less than satisfactory for detecting the state of the patient's brain because it is difficult to interpret such displays. A technique for providing an output representing the brainwaves of a person, which facilitated their interpretation, would be of great value to the anesthesiologist. Such an output would also be useful in biofeedback practices, for aiding in body control, or for entertainment purposes.